1. Field of the Invention
The field of the invention in general is an optical signal processor and in particular is an optical Fourier transformer utilizing one acousto-optical cell.
2. Description of the Prior Art
Fourier transforms are used in many fields of technology for converting information from one representation to another. Fourier transformations of time-domain signals are particularly important in signal processing such as in the fields of radar and sonar for which the one-dimensional transformation is given by ##EQU1## The function S(t) is the time-domain signal and S'(f) is the frequency-domain signal which is the Fourier transform of S(t). The conventions used to define Fourier transformations may be somewhat different from those of Eqn. (1) but they only introduce additional constants of proportionality.
For signal processing of arbitrary waveforms, the transformation of Eqn. (1) cannot be performed analytically. One available method to Fourier transform signals involves sampling the signal S(t), digitizing the samples, and then using a computer to numerically transform S(t) to S'(f). Elaborate but efficient computer codes have been written for this task under the generic name of fast Fourier transforms (FFTs). Alternatively electronic chips have been implemented which perform the parallel analog equivalent of the digital FFT.
These FFT methods, although fast, are not nearly fast enough for the requirements of evolving systems. Not only are they throughput or bandwidth limited, but they are not real-time Fourier transformers in the respect that the signal S(t) must, in general, be completed before the transformation procedure is initiated. Furthermore, the fastest electronic FFTs tend to be heavy or power-consuming.